It is widely recognized that lactic acid bacteria generally have effects of calming intestinal disorders, and many food products, such as yoghurt, and medical products, such as medicine for intestinal disorders, are available on the market.
In particular, it has become clear in recent years that lactic acid bacteria have various functions in addition to the above described effects of calming intestinal disorders, for example probiotic functions, prebiotic functions and biogenic functions.
As concerns functions of lactic acid bacteria other than those of calming intestinal disorders, prevention of hypertension, as a result of production of GABA (Non-Patent Document 1), alleviation of allergy symptoms, as a result of improvement of the immune balance when bacterial cells are ingested (Non-Patent Document 2), and elimination of Helicobacter pylori, as a result of lactic acid, which is the main product (Non-Patent Document 3) have been discovered.
In addition, there are many reports that lactic acid bacteria also have effects of preventing cancer, and particularly their effects of preventing colon cancer have been verified in experiments using animals.
There are various theories concerning the mechanism behind the colon cancer preventing effects of lactic acid bacteria, and according to one hypothesis relating to so-called pathogenic bacteria and probiotic bacteria, for example, ingestion of products containing live lactic acid bacteria or lactic acid bacteria byproducts lowers the pH in the intestines, so that probiotic bacteria, such as bifidobacteria, from among bacteria that form bacterial flora within the intestines, proliferate and pathogenic bacteria, such as Welch bacillus, are eliminated, and as a result, the inside of the intestines improves, and the occurrence of colon cancer is reduced.
According to another hypothesis, intercellular components, such as nucleic acid, bacterial wall components, such as muramyl dipeptide, and components of lactic acid bacterial bodies, such as extracellular polysaccharides, activate the immune system of the intestinal mucosa through various TLR's (toll-like receptors), and as a result, microscopic cancer cells in their initial stage are eliminated by active microphages and the like, which helps prevent colon cancer.
Furthermore, according to another hypothesis, ingested lactic acid bacteria adsorb carcinogenic substances, such as nitrosamine, which is generated as a putrefactive product within the intestine, and mutagenic substances originating from food on the surface of bacteria, so that they are discharged from the body together with the feces, and as a result, colon cancer can be prevented. According to this hypothesis, some strains of lactic acid bacteria have strong antimutagenic properties due to the effects of mutagens adsorbed in the bacterial body. Some of these are disclosed in patent gazettes (Patent Documents 1, 2, 3, 4 and 5).
In addition to the above, there is hypothesis according to which lactic acid bacteria generate anticarcinogenic substances and thus more directly prevent colon cancer, and there are reports of a phenomenon, which hints at the existence of such a substance as a result of study of yoghurt, for example. However, none of them have been corroborated, and no substance that prevents colon cancer can be specified.
There are many other hypotheses, and it can be assumed that all of these mechanisms assumed to prevent colon cancer relate to each other in varying degrees (Non-Patent Documents 4, 5, 6, 7, 8, 9 and 10).
As described above, the lactic acid bacterial components active in the prevention of colon cancer and the mechanism are not yet clearly understood, and, of course, there is no decisive proof that lactic acid bacteria have or produce antimutagenic substances. Furthermore, an effective method for producing or extracting antimutagenic substances from lactic acid bacteria has yet to be proposed.    Non-Patent Document 1: Hayakawa K. et al. Effect of a gamma-aminobutyric acid-enriched dairy product on the blood pressure of spontaneous hypertensive and normotensive Wistar-Kyoto rats. Br. J. Nutr. 2004, 92. 411-417.    Non-Patent Document. 2: Sashihara T. et al. An analysis of the effectiveness of heat-killed lactic acid bacteria in alleviating allergic diseases. J. Dairy Sci. 2006, 89. 2846-2855.    Non-Patent Document 3: Coconnier M. H. et al. Antagonistic activity against Helicobacter infection in vitro and in vivo by the human Lactobacillus acidophilus strain LB. Appl. Environ. Microviol. 1998, 64. 4573-4580.    Non-Patent Document 4: Lin D C. Probiotics as functional foods. Nutr. Clin. Pract. 2003, 18. 497-506.    Non-Patent Document 5: Ljungh A. and Wadstrom T. Lactic acid bacteria as probiotics. Curr. Issues Intest. Microbiol. 2006, 7. 73-89.    Non-Patent Document 6: Geier M S. et al. Probiotics, prebiotics and synbiotics: a role in chemo prevention for colorectal cancer? 2006, 5. 1265-1269.    Non-Patent Document 7: Hosono A. and Kashina T. Antimutagenic properties of Lactic acid-cultured milk on chemical and fecal mutagens. J. Dairy Sci. 1986, 69. 2237-2242.    Non-Patent Document 8: Sudarshan R. et. al. Effects of hydrolysis of milk glycerides on the antimutagenicity of a hexane extract of milk. J. Dairy Sci. 1998, 81. 664-671.    Non-Patent Document 9: Wollowski I. et al. Bacteria used for the production of yoghurt inactivate carcinogens and prevent DNA damage in the colon of rats. J. Nutr. 1999, 129. 77-82.    Non-Patent Document 10: Wollowski I. et al. Protective role of probiotics and prebiotics in colon cancer. Am. J. Clin. Nutr. 2001, 73. 4515-455S.    Patent Document 1: Japanese Patent No. 3209784    Patent Document 2: Japanese Patent No. 2825761    Patent Document 3: Japanese Unexamined Patent Publication H08 (1996)-056650    Patent Document 4: Japanese Unexamined Patent Publication H10 (1998)-276770    Patent Document 5: Japanese Unexamined Patent Publication H11 (1999)-113564